1. Field of the Invention
The present invention relates to a magnetic balance type current sensor using a magnetoresistive effect element (a TMR element or a GMR element).
2. Description of the Related Art
In an electric vehicle, a motor is driven with electricity, and the magnitude of a current for driving a motor is detected by, for example, a current sensor. As the current sensor, for example, a magnetic balance type current sensor, in which a circular magnetic core that collects a magnetic flux due to a current to be measured is provided around a conductor, a magnetic detecting element is disposed at a core gap (cut-out portion) of the magnetic core, and a negative feedback coil is wound around a circular portion of the magnetic core, is disclosed (for example, refer to Japanese Unexamined Patent Application Publication No. 2004-279226).
The magnetic balance type current sensor disclosed in Japanese Unexamined Patent Application Publication No. 2004-279226 is operated in such a manner that when a current flows to the conductor, an output from the magnetic detecting element is converted into a current and is fed back to the negative feedback coil, and an induced magnetic field due to a current to be measured is canceled by a cancel magnetic field that is generated in the negative feedback coil, and then the current that flows through the negative feedback coil is taken out as an output. In addition, this current sensor is provided with a reset circuit portion that allows a saturation remanent magnetization to stably occur with respect to the magnetic core, and suppresses an output fluctuation due to a variation in the remanent magnetization during power supply start-up or an abnormal decrease in power supply.
However, in the magnetic balance type current sensor disclosed in Japanese Unexamined Patent Application Publication No. 2004-279226, measurement accuracy is improved through adjustment of the remanent magnetism, but hysteresis occurs due to an effect of the remanent magnetism. Furthermore, since the magnetic balance type current sensor is provided with the magnetic core, miniaturization is not realized, and it is necessary to provide the conductor, which allows a current to be measured to flow, at the inner side of the magnetic core. Therefore, there is a problem in that workability deteriorates during installation.